BJT-like transistor symbol - unknown meaning?

Discussion in 'General Electronics Chat' started by sbixby, Jul 11, 2012.

  1. sbixby

    Thread Starter Active Member

    May 8, 2010
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    Attached is a snip from a Texas Instruments datasheet for the 74*04 hex inverter chip.

    There are three types represented in the datasheet - 7404, 74LS04, 74S04; the original TTL circuit uses the standard BJT transistor symbol, but the other two use a symbol (attached) that I can't seem to find.

    What is it??

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    By way of explanation, I am working through the AAC book (V4, C3, S2) about "The NOT Gate" and mocking it up in a simulator for sake of understanding the operation of the circuit. (I'm still fuzzy on BJTs, so I like to work through the gate circuits at this level to help strengthen my understanding.) Since the AAC page doesn't show values for the resistors, I though I'd borrow one of the datasheets' values for my simulation.
     
  2. crutschow

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    Mar 14, 2008
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  3. Papabravo

    Expert

    Feb 24, 2006
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    The "S" in the part numbers stands for Schottky. The p-n junctions are implemented with Schottky barriers that have a lower forward voltage drop.
     
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  4. sbixby

    Thread Starter Active Member

    May 8, 2010
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    So, then, a related question - is a "Schottky transistor" a discrete part that I could look up for operating curves? I'm not finding one offhand.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    If you look at my reference you will see that is not quite correct. ;) A Schottky transistor is a standard junction transistor with a Schottky diode between the base and collection to limit saturation of the transistor and minimize saturation delay.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    No, it is not a discrete part you can buy. You can emulate one by placing a small Schottky diode between the base and collector of a small switching-type BJT as shown in the reference.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    Ah..yes right you are. It is something that is easy to fabricate on a chip however.
     
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